1.Complex of antibodies with Hen Eggwhite Lysozyme. The Fab of the HyHEL-5 antibody to lysozyme in recombinant form has been crystallized. These crystals diffract to a resolution of 1.7A, vs 2.6A for the previous, proteolytically prepared material. This much higher resolution enables us to study in much more detail the interaction between antibody and antigen and refinement of the structure has been completed. The refined structure is now being analyzed. 2. Triple-helix DNA We have now determined the three-dimensional structure of an oligodeoxynucleotide which exibits a triplex form of association. This structure has been determined a 1.7A resolution. This is the first determination of a significant stretch of triplex DNA. 3. MarA-DNA complex MarA is a transcriptional activator of the mar operon that renders E. coli resistant to a variety of antibiotics. There is no structural information availableabout MarA, nor about the AraC subfamily, transcriptional regulators that have high sequence homology with MarA. We have determined the crystal structure of MarA complexed with its DNA binding site. The complex crystallized in a form that diffracted to 2.3A at the NSLS synchrotron, and the structure was determined by MAD phasing based on bromine substitution.